Research Article

Orderly compartmental mapping of premotor inhibition in the developing zebrafish spinal cord

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Science  23 Oct 2020:
Vol. 370, Issue 6515, pp. 431-436
DOI: 10.1126/science.abb4608

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Spinal circuit development

Motor neuron circuits in the zebrafish spinal cord support both the rapid evasion response and the leisurely swimming response. Kishore et al. now follow the development of inhibitory interneurons as these circuits are assembled in the larva. Interneurons generated early in development drive different sorts of circuits and synapse onto different subcellular sections of the motor neurons than interneurons generated later in development. Thus, both rapid evasion and slower swimming are supported by the same cellular components assembled in different ways. The authors suggest that development follows an opportunistic rule in which interneurons synapse onto what is available to them at that moment in development.

Science, this issue p. 431

Abstract

In vertebrates, faster movements involve the orderly recruitment of different types of spinal motor neurons. However, it is not known how premotor inhibitory circuits are organized to ensure alternating motor output at different movement speeds. We found that different types of commissural inhibitory interneurons in zebrafish form compartmental microcircuits during development that align inhibitory strength and recruitment order. Axonal microcircuits develop first and provide the most potent premotor inhibition during the fastest movements, followed by perisomatic microcircuits, and then dendritic microcircuits that provide the weakest inhibition during the slowest movements. The conversion of a temporal sequence of neuronal development into a spatial pattern of inhibitory connections provides an “ontogenotopic” solution to the problem of shaping spinal motor output at different speeds of movement.

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